Previous work has shown that substructures in the BH mass distribution can be captured by cubic splines acting as a perturbation on top of a simpler parameteric model [1]}, [2]}. In this work, we model the spin magnitude and tilt distributions using cubic splines to obtain a more data-driven result for the inferred population of BH spins. In doing so, we limit the potential bias caused by mismodeling the spin distribution and allow for the possibility of capturing features not accessible with a parametric model.
